Is there really such a strong correlation? Naturists probably are likely to come from "less Victorian" social circles, but some quite significant group is actually rather sex-phobic, precisely because of a (real or imagined, but definitely perceived) threat from those bad apples. Maybe there are a lot of regional differences as well - I imagine the "old guard" being rather sexually liberated in the San Francisco region, for instance.
+++ man, exactly what I was about to say. I don't see nowadays naturists more sexual-orientated than the nowadays average among the whole society. It might be a confusion felt by some people who link naturism with the Hippie times where those people's colourful lives involved both a lot of nudity and a lot of sex.
What is really intriguing for me these days is the big hypocrisy of media, commercials, going soooooo much deeper into body exposure nowadays than a few decades ago and in the same time perceiving nudism as something so rare, bizarre, inappropriate, etc. The same modest housewife might find it OK that both the actress in a bra commercial shown on a billboard in the city as well as the female moderator of a TV show have their breasts barely covered, purely to gather more attention on purpose, but if she got to know that her neighbouring housewife had gone to a nude beach, just for her own relax, not for other's attention, she'd call her names... ah yeah, I dislike such double standards!